Not true in the US for Apple or any other product. Apple's written IPod warranty provides an exclusion "(f) to damage caused by service (including upgrades and expansions) performed by anyone who is not a representative of Apple or an Apple Authorized Service Provider (“AASP”);" but not for merely having such service done. The other Apple hardware documents are similar.

It is perfectly reasonable for Apple, Nikon, or anyone else to exclude waranty coverage for damage done by others, but it is illegal to void a warranty for using independent service or after market parts, unless they cause damage, and only to the extent of that damage.
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Lee Baylin